The present invention relates to a planar linear pulse motor, and more particularly relates to a planar linear pulse motor, of a type which is suitable for application for driving the movement of the magnetic head or heads in a floppy disk drive of a word porcessor or a personal computer or the like, which is improved in terms of thinness, overall size, assemblability, manufacturability, mountability, operational accuracy, and speed of operation.
In the prior art, especially with regard to application to a floppy disk drive of a word processor or a personal computer or the like, there have been proposed various types of linear pulse motor; a cylindrical type of linear pulse motor is typically used. In Japanese Utility Model Laying Open Publication Serial No. 58-97759 (1983), which it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, and a typical figure of which publication is shown in FIG. 4 of the accompanying drawings in a sectional view longitudinal from the point of view of its direction of moving operation, there is disclosed a cylindrical linear pulse motor comprising a stationary hollow cylindrical housing member 6 formed with a set of magnetic pole teeth denoted as 61 on its inner cylindrical surface, and a movable member 7 is slidably supported on a guide shaft 62, which extends substantially along the central axis of said cylindrical housing member 6, by a bearing construction 71 incorporating a bearing bush 72. This movable member 7 is formed with magnetic pole teeth 73 on its outer cylindrical surface, which cooperate with the magnetic pole teeth 61 of the cylindrical housing member 6 to linearly drive the movable member 7, according to suitable and selective magnetization of the movable member 7 in a per se known manner.
However, such a conventional type of cylindrical linear pulse motor is fraught with the disadvantage of a large external diameter, because of the necessarily coaxial disposition of the guide shaft 62, the bearing construction 71 and its bush 72, and the magnetic pole teeth 73 and 61 and the cylindrical housing member 6; and, further, it is difficult to raise the production efficiency of such a conventional type of cylindrical linear pulse motor to a realistically high level, because the magnetic pole teeth 61 of the cylindrical housing member 6 and the magnetic pole teeth 73 of the movable member 7 must be formed by machining using a machine tool. Further, the accuracy for assembly required is also very high, which imposes a time and cost penalty. Accordingly the cost of the finished cylindrical linear pulse motor is inevitably higher than desirable.
Further, in Japanese Patent Laying Open Publication Serial No. 59-89565 (1983), which again it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, and typical figures of which publication are shown in FIGS. 8 and 9 of the accompanying drawings, respectively in an exploded perspective view and in a sectional view longitudinal from the point of view of its direction of moving operation, there is disclosed a planar type linear pulse motor comprising a stationary assembly 1 and a planar movable member 5. The stationary assembly 1 and the movable member 5 thereof are mounted so as to be mutually slidable as shown by the arrow "A" in FIG. 8 by a means not particularly shown in the figures. The lower surface (not visible in the figure) of the planar movable member 5 is formed with a series 51 of magnetic pole teeth which are set in series at a pitch of P; and, as before, each of the magnetic pole teeth of this series 51 thereof is continuous from the left side to the right side thereof.
And the stationary assembly 1 comprises a plate shaped permanent magnet 2, having magnetic poles on its opposite side surfaces which are different in polarity but are the same along each said side surface, and extending substantially perpendicular to the direction of sliding motion of the planar movable member 5. A pair of magnetic core members 31a and 31b are provided, each being generally shaped like a letter "C", with central portions thereof denoted respectively as 31c and 31d being narrowed down somewhat and having coils 32a and 32b wound on them. Under the end portions 39a, 39b, 39c, and 39d of these magnetic core members and in the transverse direction there is fixed the permanent magnet 2, for example by bonding. And a back yoke 115 is fixed under the permanent magnet 2 for supporting it. The end portions 39a through 39d of the magnetic core members 31a and 31b are respectively formed directly as magnetic pole teeth portions 42a, 42b, 42c, and 42d with the upper surfaces thereof each being formed with a series of magnetic pole teeth 42a through 42d respectively, each said series being set at the same pitch P, and with the phases of the four series of magnetic pole teeth 42 arranged along the four magnetic pole teeth portions 42a, 42c, 42b, and 42d being staggered apart by a phase difference of P/4 in that order. By appropriately changing the direction of the electric current supplied to the coils 32a and 32b, the four magnetic pole teeth portions 42a, 42c, 42b, and 42d are sequentially magnetized in the one or the other polarity as required, and in cooperation with the magnetic biasing effect provided by the permanent magnet 2 they function to pull the planar movable member 5 along by its teeth 51 relative to the stationary assembly 1 by increments of one quarter of the pitch P of said teeth 51.
However, such a type of planar linear pulse motor is fraught with the disadvantage of an inevitably excessive thickness, because the permanent magnet 2 and the back yoke 115 are layered together over the rear surfaces (the lower surface as seen in FIG. 8) of the magnetic core members 31a and 31b. Particular problems would arise when applying such a type of planar linear pulse motor for driving the movement of the magnetic head or heads in a floppy disk drive of a word processor or a personal computer or the like. For example, as schematically shown in FIG. 9 of the accompanying drawings in longitudinal sectional view, when a mounting structure for such a magnetic head 117 of a floppy disk drive is utilized, since said magnetic head 117 must be supported from the planar movable member 5 of the planar linear pulse motor by way of a mount 118, and since the back yoke 115 and the permanent magnet 2 are layered together against the magnetic core members 31a and 31b, the overall thickness (height H as seen in the figure) of the device from the base 119 on which it is mounted to the floppy disk 120 inserted into the floppy disk drive is inevitably great. In fact, this is one of the major difficulties relating to reducing the thickness of a planar linear pulse motor. Accordingly, low profile design of such a floppy disk drive is well nigh impossible when such a planar linear pulse motor is to be incorporated therein, since the pulse motor itself it relatively thick.
Another problem that arises in connection with the manufacture of such a planar linear pulse motor relates to the assembly thereof. As is for example disclosed in Japanese Patent Laying Open Publication Serial No. 60-113652 (1984), which again it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, a conceivable construction for such a planar linear pulse motor could be for a stationary member or base plate to be provided, and for a permanent magnet and four groups of magnetic pole teeth to be supported on said base plate. And a guide mechanism for the planar movable member of the planar linear pulse motor could be provided, with a prestressing mechanism biasing said guide mechanism against said planar movable member and thus holding said planar movable member in a slidable manner. However, the problem would arise with such a construction that, since the permanent magnet and four groups of magnetic pole teeth would be required to be located on said base plate during manufacture, the positioning of said permanent magnet and said magnetic pole teeth during manufacture of the planar linear pulse motor could be rather difficult.
Conventional linear pulse motors have not typically had any positioning mechanism for mounting them into other equipment. When a linear pulse motor is to be installed into a system such for instance as a floppy head drive for a floppy disk drive for a word processor or a personal computer or the like, the advance shaft for the linear pulse motor and the central rotary shaft of the floppy disk drive must cross each other at right angles, and should any shifting or misalignment develop therebetween reading of information from the floppy disk loaded in the drive would inevitably become impossible. Therefore normally when a linear pulse motor is to be installed into an apparatus such as a floppy disk drive, a high precision mounting jig is prepared, and the positioning of the linear pulse motor with respect to said apparatus is conducted with the aid of this jig prior to the actual mounting of the linear pulse motor. The use of such a jig means a requirement for extra time for the assembly of the device, and the need for a jig and the work required for preparing it inevitably raise the overall manufacturing cost.
Another problem that arises in connection with the manufacture of such a planar linear pulse motor relates to the detection of the position of the planar movable member thereof.
According to a conventional magnetic head drive device for a floppy disk drive such as the one shown in FIG. 17 of the accompanying drawings in perspective view, a feed screw thread 41 is formed on a rotary shaft of a rotary pulse motor 4 while a screw thread hole 52 is formed in a support plate 5 which supports a magnetic head 6 and is supported by a straight guide, and the feed screw thread 41 is engaged to the screw thread hole 52 so as to convert the rotary motion of the pulse motor 4 into the linear motion of the magnetic head assembly 6. However, according to this conventional device, the origin or the start of the travel of the pulse motor 4 is defined at the outer most track of the floppy disk 7 fitted in the device by attaching a light shielding plate 53 to a part of the magnetic head support plate 5 and by placing a photo sensor unit 8 on the traveling path of this light shielding plate 53 so as to permit the adjustment of the light shielding position for the purpose of defining the relative position of the magnetic head 6 and the floppy disk 7. However, according to this method of defining the origin or start of travel of the pulse motor 4, it is necessary to adjust the position of the photosensor unit 8 while looking at the signal output by the magnetic head assembly 6 from the floppy disk 7, after all the parts such as the pulse motor 4, the magnetic head support plate 5 and so on have been installed into the device, and this adjustment requires considerable effort. Furthermore, the photosensor unit 8 is typically one which is an off the shelf product which is large in external dimensions and is expensive, and this fact contributes to the large size and the high price of such a device. It has been proposed to apply a direct action type planar linear motor to such a magnetic head drive device, as for example in the previously discussed Japanese Patent Laying Open Publication No. 59-89565, but its travel origin detection mechanism is similar to the above described one, and the definition of the origin or start of travel thereof gives rise to similar problems.